Production of sulfur dioxide



06b 1956 w. K. LEWIS ETAL 2,766,102

PRODUCTION OF SULFUR DIOXIDE Original Filed Dec. 25, 1948 Qrren Lewis Ed mwammm gnventors By Q q'tt or neg PRODUCTION OF SULFUR DIOXIDE Warren K. Lewis, Newton, and Edwin R. Gilliland,

Arlington, Mass., assignors to Esso Research and Engineering Company, a corporation of Delaware 14 Claims. (Cl. 23-177) This application is a division of Serial No. 66,702, filed December 23, 1948, now forfeited. The present invention is directed to the production of S02 from sulfurcontaining solids, particularly sulfur-containing minerals such as sulfidic ores including various pyrites, preferably iron pyrites, naturally occurring elemental sulfur or materials rich in elemental sulfur, hydrogen sulfide, etc.

Prior to the present invention, S02 has been produced commercially by the combustion of sulfur or sulfur-containing raw materials with air. The use of air as the oxidizing gas results in the formation of a product gas containing large amounts of nitrogen which acts as a diluent of the S02 produced. The product S02 may be, and has heretofore been separated from nitrogen by absorption in suitable aqueous solutions. However, absorption of S02 in this manner has encountered serious difliculties resulting from the extreme corrosiveness of the SO2-liqu0rs formed as well as from the large proportions of inert gases present. S02 may be produced nitrogen-free by the use of pure oxygen as the oxidizing agent, however only at a commercially prohibitive cost.

Serious problems also arise when it is desired to produce S02 substantially free of S03, 02 and free sulfur. It is practically impossible so to control the feed of sulfur and oxidizing gas to the burner that these two reactants are at all times present in the theoretical stoichiometn'cal proportions required for a complete conversion of the sulfur feed into S02 only. However, even if this theoretical proportion could be maintained constantly in the charge to the reactor this would still not avoid some of the sulfur going to S03 and some not being oxidized at all, so that the burner eflluent always will contain 803, S and O2 in addition to the nitrogen from the air. These impurities entail various serious disadvantages. Sulfur vapor condenses on the cooling surfaces used in cooling the burner gases, reduces cooling efliciency and reduces the yield of S02. Excess oxygen oxidizes S02 to S03 which is likewise undesirable because it reduces the yield of desired product and interferes with the operation of the process.

A large proportion of the S02 used is recovered in the roasting of sulfidic ores, particularly iron and zinc ores for metallurigical purposes. A complete removal of the sulfur from the ore is of greatest importance in these cases, because residual sulfur renders the cinder unsuitable for many purposes, for example as charge to blast furnaces, as catalyst, etc. This is diflicult to accomplish by prior art processes.

The present invention eliminates the above mentioned difliculties and affords various additional advantages. These advantages, the nature of the invention and the manner in which it is carried out will be fully understood from the following description thereof read with reference to the accompanying drawing which shows a semi-diagrammatic view of a system adapted to carry out the invention.

It is, therefore, the principal object of the present invention to provide means for producing from sulfidic raw nited rates Patent 6 materials, such as sulfidic ores, elemental sulfur, or the like, an S02 product which is substantially free of nitrogen, S03, oxygen, and elemental sulfur. An additional object of the invention is to insure complete re moval of sulfur from sulfidic ores used as the starting material while still recovering S02 free of the objectionable impurities mentioned above. Other objects and advantages will appear hereinafter.

In accordance with the present invention solid oxygen carriers, particularly metal oxides which remain solid and will not sinter at suitable sulfide roasting and sulfur burning temperatures and which may be readily regenerated by oxidation with air below the sintering temperature are used in place of air for the oxidation of the sulfidic raw materials. These oxygen carriers preferably should have an oxidizing potential sufficient to oxidize sulfur completely to S02 but insuflicient for oxidation beyond that stage. Higher oxides of iron, particularly ferric oxide (FezOa) and various oxidic iron ores rich in F2O3 or mixtures of FezOs with Fe3O4 are typical examples of the preferred oxygen carriers of the invention.

The solid oxygen carriers of the invention are preferably employed in a finely divided form and contacted with the sulfidic raw materials in a fluidized condition, i. e. in the form of a dense highly turbulent mass of subdivided solids fluidized by an upwardly flowing gas to resemble a boiling liquid having a well defined upper level. The sulfidic raw materials are used either in the vapor state or likewise as finely divided solids.

The fluidized state of the reactants affords perfect contact betwen solids and solids and gases, ideal temperature control and greatest uniformity of reactant distribution throughout the fluidized mass. As a result, the process is an extremely flexible one and may be readily controlled. Oxygen available in the form of metal oxide can be chosen so that oxidation of S02 to S03 is negligible at the prevailing reaction conditions while at the same time oxidation to S02 is complete. The absence of air eliminates the danger of S02 dilution With inerts.

In order to obtain proper fiuidization all solid reactants should be ground to a size such that substantially all of it will pass through mesh screen. For the best results the ground solids should include a Wide range of particle sizes ranging upwardly from about 20 microns to about 100 mesh with a large proportion of material between about 200 and 400 mesh.

Fluidization is accomplished by means of S02 introduced into the reaction zone and by the S02 produced in the course of the reaction. If desired, product S02 may be recycled for this purpose to a lower portion of the reacting solids mass. Superficial linear flow velocities of the fluidizing gases within the fluidized bed may vary between about 0.3 and 3 ft. per second for proper fluidization of most practical solid reactants at the particle sizes specified above.

Spent solid oxygen carrier may be intermittently or continuously reoxidized with air in the same or a separate reactor and returned to the S02 generation step. in accordance with the preferred embodiment of the invention the spent oxygen carrier consists predominantly of R304 which is contacted in the fluidized state with air to be reoxidized to FezOa or mixtures thereof with the lower oxide and thereafter returned to the S02 generation step. This reoxidized material is substantially sulfur free and when sulfidic iron ores are used as the raw materials it may be employed in blast furnaces, for catalysts, etc. Since the reoxidation reaction is highly exothermic at least a substantial part of the heat required for the sulfur oxidation by the iron oxide may be generated in the reoxidation stage and supplied to the sulfur dioxide generation in the form of sensible heat of reoxidized iron oxide.

It has been found that sulfur vapor will react with oxides of iron at an extremely high rate above a temperature level of 600-700 C. to form FeS and S02. The former begins to react with FezOa above about 700 C. to form Fes04 and pure S02, the rate becoming very satisfactory at about 800 C. It has further been found that the rate is particularly high in the presence of S02. Consequently, any FeS present in the bed is eliminated very rapidly, provided there is an excess of FezOs. Since sintering of the iron compounds involved becomes appre ciable at temperatures substantially above 900 C., it is preferred to use temperatures between the approximate limits of 700 and 900 C. for the conversion of sulfur vapors of sulfidic sulfur into S02 in accordance with the present invention. The reoxidation reaction may be carried out at slightly higher temperatures, but still below sintering temperature, say, at about S50l 100 C.

In order to assure high reaction rates and to carry sulfur oxidation in the S02 generator as far as possible in accordance with the findings just referred to, it is preferable to employ a substantial stoichiomctrical excess of F6203 over the oxidizable sulfur present, although it has been found that even at an FezOa concentration as low as 15% of the total solids the hourly sulfur oxidation rate at 800 C. is still about 30% of the total sulfide sulfur present at the time, even in the presence of very dilute S02.

Having set forth its objects and general nature, the invention will be best understood from the more detailed description hereinafter, in which reference will be made to the accompanying drawing.

Referring now in detail to the drawing, numeral 1 designates a hopper for ground sulfldic material which, for the purposes of illustration, may be assumed to be 5652 in the form of pyrite ore. The drop leg 2 is provided with a suitable feed control valve 4 and also with aeration taps 3 to facilitate the flow of the powdered material through drop leg 2.

Generator 5 is provided near its bottom, preferably below the discharge point of drop leg 2 with a perforated distributing means or grid 7. A gas feed line 9 enters generator 5 below grid 7. A gas-solids separator such as cyclone 11 provided with a solids return pipe 13 may be arranged in the upper portion of generator 5. The middle section of generator 5 may be provided with conventional heat exchange means such as coil 15 for the purpose of heating or cooling as desired. A product gas withdrawal pipe 17 leads away from cyclone 11.

A solids transfer line leads from a bottom drawotf well 19 in generator 5 to an upper portion of a metal oxide regenerator 25. Transfer line 20 is provided with a flow control valve 21 and aeration taps 23. Regenerator 25 may be of a design generally similar to that of generator 5. A grid 27, a gas feed line 29, a cyclone 31, a solids return pipe 33, a heat exchange coil 35, a gas Withdrawal pipe 37 and a bottom drawotf well 39 are arranged in a manner similar to that outlined in connection with generator 5. A solids transfer line 40 provided with control valve 41 and aeration taps 43 leads from Well 39 to an upper portion of generator 5.

A soaking vessel 45 may be connected over lines 44 and 60 to transfer line 20. Soaker 45 may be provided with grid 47, gas feed line 49, cyclone 51, solids return pipe 53, heat exchange coil 55, gas withdrawal pipe 57 and solids drawoff well 59.

In starting the operation using FeS z as the sulfidic raw material and FezOs as the oxidizing agent, generator 5 contains above grid 7 a dense fluidized mass consisting substantially of F6203 having a particle size of about 200-400 mesh at a temperature of about 700-900 C. Preheat may be supplied by means of coil 15 and of preheated air or nitrogen supplied through line 9, the latter serving simultaneously to fluidize the solids mass during the starting period. When the desired operating temperature is reached the air supply through line 9 is replaced by S02.

When reaction between FeSz and FezOa sets in, S02 may be recycled from line 17 through lines 18 and 9 to the bottom of generator 5 to provide proper fluidization. The superficial linear gas velocity Within generator 5 is preferably maintained at about 0.5-1.5 ft. per second to establish an apparent bed density of about 4050 lbs. per cu. ft. and a bed height between grid 7 and level L5 of about 520 ft.

Substantially pure 502 containing suspended solids fines flows overhead from level L5 at a linear velocity at that level of about 0.5-2 ft. per second, passes through cyclone 11 and is recovered through line 17, free of entrained solids, to be further Worked up by compression and/ or absorption in conventional means (not shown). A portion of the S02, amounting to about /3 to /3 of that discharged through line 17 may be recycled through line 18 for fluidization. Solids separated in cyclone 11 may be returned to the fluidized mass through pipe 13. Particles of undesirable small size or excess may be discarded through line 14. Product gas is recovered through line 17a.

It is preferred to operate the S02 generator bed with not less than 15 FezOa in the solids. If the FezOs is consumed completely out of these solids it has been found impossible to oxidize the sulfur completely to S02 and then some sulfur vapor is always left in the gas. However, so long as a substantial amount, such as l520%, of FezOs remains in the bed, one can oxidize sulfur largely to S02 provided the sulfur feed to the generator is sulfur vapor or a compound such as FeSz, which at the temperature of the bed will give off sulfur. The sulfur content of the gas thus produced is never more than of the order of 1%. However, this is doubly undesirable because under these conditions iron sulfide is accumulating in the bed. This will then flow to regenerator 2S and be evolved there as dilute S02 gas.

Spent solids which may consist essentially of lower iron oxides, chiefly PC1504, but may contain as much as 70% F6203 depending on the temperature difference between vessels 5 and 25, are withdrawn from well 19 and may be passed under the pseudo-hydrostatic pressure of the fluidized mass in generator 5, through line 20 directly into an upper portion of regenerator 25. Air which may be, but usually is not, preheated to about 800-l000 F. in any conventional manner, is supplied through line 29 to fluidize and oxidize the solids in regenerator 25 to rcconvert the solids substantially completely to FezOa. The air requirement of the system is usually very little in excess of that required for the oxidation to S02, of whatever form of sulfur is fed. The excess rarely exceeds 10% and is kept down because of the expenses involved in blowing it against the pressure head of the bed of solids in vessel 25.

It is desirable to operate regenerator 25 at the highest temperature compatible with good fluidization. If the iron oxide employed is impure the sintering temperature may be low and the temperature in vessel 25 must be kept down accordingly. The use of pure iron oxide has the advantage of permitting higher temperatures in vessel 25 because this in turn greatly reduces the recycle rate of the solids from vessel 25 to vessel 5 because the higher temperature dilference between vessel 25 and'vessel 5 increa es the heat carrying capacity of the recycling solids. The fluidization conditions may be about the same as specified for generator 5. Temperature control may be accomplished by means of cooling coil 35 in any manner known per se. A mixture of residual air, S02. and S03 is withdrawn from level L25 through cyclone 31 and pipe 37 to be used for any desired purpose.

Regenerated iron oxide is withdrawn from well 39 and passed under the pseudohydrostatic pressure and substantially at the temperature of the fluidized mass in regenerator 25, through line 40 to an upper portion of generator 5. The sensible heat of the solids flowing through line 40 is normally of a slightly higher temperature than that of the solids in generator 5 so that substantially all the heat required in generator 5 may be supplied by circulating adequate amounts of solids from regenerator 25 to generator 5. A solids circulation rate of about 60-75 lbs. between vessel 5 and 25 per pound of FeSz charged is generally suflicient to satisfy the oxygen and heat requirements of the system when most of the S02 product is taken off in 17a. This rate can be reduced very substantially when it is practicable to hold a high temperature differential between 25 and 5. It can also be reduced even more when a considerable fraction of the sulfur fed to the system is taken overhead out of regenerator 25 as dilute gas. Heat may be added or withdrawn through coil as required.

In order to maintain satisfactory oxidation rates in generator 5, it is generally advisable so to control the solids circulation rate that the Fe203 content of the fluidized mass in generator 5 will not drop substantially below 15% by weight, because the oxidation rate of FeS falls 01f sharply below this concentration level. At Fe2O3 concentrations above about 15%, the rate of FeS oxidation lies substantially above 30%, and may reach even well over 100%, per hour of the amount of FeS in the bed.

The rate of reaction in regenerator 25 at the temperature levels specified is extremely high. Apparently the first reaction is oxidation of FeS. However, in good operation the entering FeS concentration in the oxides is very low so that the oxidation of any FE3O4 present goes on rapidly. The latter consumes oxygen so rapidly that all or" it is removed from the air practically quantitatively by conversion to FezOs.

In accordance with a desirable modification of the process of the invention, part or all of the spent solids withdrawn from generator 5 may be passed through line 44 to a fluidized soaking vessel 45 to permit prolonged contact of sulfide with iron oxide and a substantial sulfur clean-up. If desired, small amounts of air may be admitted through line 49 to complete the oxidation and aid fluidization but without substantial re oxidation of Fe304 to FezOa. If pure S02 is to be produced in soaker 45, product S02 may be led from line 48 through line 49 to the bottom of soaker 45. The additional gas produced in soaker 45 is withdrawn through line 57 and may be either separately collected or combined with the product gas recovered through line 17. Spent soaker solids may be withdrawn from well 59 and returned via line 60 to line and regenerator 25. An aeration gas may be injected through tap 63 to promote the solids flow indicated. Soaking times of about 20-30 minutes are generally suthcient for substantially complete sulfur cleanup to form a sulfur-free iron product.

It will be appreciated that the process described above may be made fully continuous by continuously charging FeSz, continuously withdrawing S02 and continuously circulating solids between vessels 5 and 25, excess solids being Withdrawn from the system through line 65 or any other suitable withdrawal means.

The system illustrated in the drawing permits of various modifications. Sulfur vapor rather than solid sulfides may be used as the sulfidic starting materials. Such vapors may be introduced into the system through line 9. All other reaction conditions and procedural steps are substantially analogous to those described above. Sulfurburning plants frequently have numerous different uses for the S02 produced and the relative demand for the difierent purposes may vary widely. The system described with reference to the drawing lends itself with extraordinary flexibility to such a situation. When the demand is primarily for liquid S02, this system will be operated so that practically all the product goes out line 17a. If the demand for S02 goes down, FeS can be al lowed to move over to vessel and the dilute gas produced in vessel 25 may be used for other purposes. If the other demand, is, e. g. for sulfite the air supply through line 29 will be limited so that the gas going out line 37 is 02-free. In other words, reoxidation of the solids in vessel 25 will be somewhat incomplete. If the other demand is for H2804, excess air can be used in line 29 and the gases from line 37 sent to the H2804 plant. If the demand for both liquid S02 and other products rises simultaneously one can increase the pure S02 production from line 17a by using lower sulfur oxidation in vessel 5 and allowing a fairly high concentration of FeS, up as high as 8% by weight of the circulating solid, to vessel 25 where this FeS will be burnt by air, the corresponding sulfur coming off as a dilute gas. However, for the production of pure S02 as the principal product FeS circulation from vessel 5 to vessel 25 is kept at a minimum, usually corresponding to less than 5% of the total sulfur fed to the system.

i t may be desirable to operate the solid circulation lines so as to secure a substantially theoretical yield of high purity S02 through line 17a. To do this, a small amount of N2 may be brought over to vessel 5 from the air entering vessel 25. By cooling and/or compressing the gas leaving line 17a, the S02 is condensed out in large degrees and the N2 can be recycled to lines 9 and 49. This soon builds up an N2 concentration in vessel 5 which will hold the system in N2 balance. If completely pure S02 is desired in line 17a, some S02 is allowed to drift to vessels 45 and 25. This S02 leaves these vessels as dilute gas which, however, is satisfactory for many purposes.

Solids circulation between the vessels 5, 25 and 45 may also be accomplished by arranging the vessels at different levels and using standpipes and dilute solids-in-gas suspensions to accomplish downward and upward flow,

respectively, in a manner known in the art of fluid solids handling.

It will be understood that the gases used for aerating the various solids transfer lines may also act as stripping gases and should be selected so as not to interfere with the reactions intended in the vessels to which the solids are transferred. For example taps 3, 43 and 46 should be supplied preferably with S02, While air may be used for taps 23 and 63.

While a system including two or more vessels of the type illustrated is essential for a continuous production of S02, it is noted that intermittent operation carried out in a single vessel in a make and blow manner is likewise within the scope of the present invention. In this case the make period will be operated substantially at the conditions outlined above for generator 5 and the blow period at those outlined above for regenerator 25, as will be readily understood by those skilled in the art.

While the foregoing description has referred to oxides of iron as the preferred oxygen carrier of the invention, it is noted that other solid oxygen carriers may be employed in a generally analogous manner. However, in choosing such other oxygen carriers it is imperative to choose carriers with the proper oxidizing potential and with a limited tendency to sulfide formation. It is also preferable to avoid oxygen carriers which, under the conditions of operation, can form low melting compounds. A compound which is satisfactory in these respects is M11304. Copper oxide is also suitable for the purposes of the invention.

Other modifications obvious to those skilled in the art are within the scope of the invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

What is claimed is:

l. A process for producing S02 substantially free of sulfur trioxide, oxygen, nitrogen, and elemental sulfur which comprises intimately contacting a naturally-occurring sulfur-containing material in a densely fluidized bed supported on a grid in a generation zone with a finelydivided solid metal oxide having an oxidizing potential sutficient to oxidize sulfur substantially completely to S02 but insufficient for sulfur oxidation beyond S02 under .zone at a temperature of 600 the reacted conditions of the process, at an elevated temperature sufficient to cause the aforesaid formation of S02 but below the sintering temperature of the metal oxide, whereby the oxygen of the metal oxide reacts with the sulfur of said sulfur-containing material to form S02 and a metal oxide of reduced oxygen content, passing S02 vapors upwardly through said grid at a rate sufficient to maintain the finely-divided solid oxide in the generation zone in a fluidized state, and withdrawing S02 product from the generation zone.

2. A process according to claim 1 in which the sulfurcontaining material is sulfur.

3. A process for producing S02 substantially free of sulfur trioxide, oxygen, nitrogen, and elemental sulfur which comprises intimately contacting a normally solid naturally-occurring sulfur-containing material in a generation zone with a finely-divided solid metal oxide having an oxidizing potential sufficient to oxidize sulfur substantially completely to S02 but insuflicient for sulfur oxidation beyond S02, at an oxidizing temperature above about 600 C. but below the sintering temperature of the metal oxide, whereby the oxygen of the metal oxide reacts with the sulfur of said sulfur-containing material to form 502 and a metal oxide of reduced oxygen content, passing S02 vapors upwardly through the finelydivided solid oxide in the generation zone at a rate sufficient to maintain said oxide as a dense turbulent fluidized mass, withdrawing S02 from the generation zone, removing the metal oxide of reduced oxygen content to a separate regeneration zone, rcoxidizing the withdrawn oxide by contacting the same with an oxygen-containing gas in the regeneration zone, purging the reoxidized oxide with S02 and returning the reoxidized oxide fluidized in S02 to the generation zone.

4. A process according to claim 3 in which the metal oxide is one selected from the group consisting of ferric oxide, manganese oxide (M11304), and copper oxide.

5. A process for producing substantially pure S02 which comprises intimately contacting a sulfidic ore in a generation zone with finely-divided Fe2O3 as essentially the sole oxidizing agent at a temperature of 600 C, to 900 C. whereby reaction sets in between the sulfurcontaining ore and Fe203 to form S02 and F0304, passing S02 vapors upwardly through the finely-divided solids in the generation zone at a rate sufiicient to maintain said solids as a dense turbulent fluidized mass, and withdrawing substantially pure S02 from the generation zone.

6. A process according to claim 5 in which at least 15 weight percent Fe203 based on total fluidized solids present is maintained in the generation zone at all times.

7. A process according to claim 5 in which the sultidic ore is iron pyrites.

8. A process for producing substantially pure S02 which comprises intimately contacting a naturally-occurring sulfur-containing ore with finely-divided F6203 as essentially the sole oxidizing agent in a generation C. to 900 C. whereby reaction sets in between the FezOs and the sulfur-containing ore to form S02 and F6304, passing S02 vapors upwardly through the finely-divided solid in the generation zone at a rate sufficient to maintain said solid in a fluidized state, withdrawing substantially pure S02 from the generation zone, withdrawing a stream of solid containing FesOi from the generation zone, contacting the withdrawn stream of solid in a regeneration zone with an oxygen-containing gas to reoxidize the solid to FezOs, purging the reoxidized solid by means of S02 vapors and re-introducing the R203 fluidized in S02 to the generation zone.

9. A process according to claim 8 in which at least 15 weight percent of FezOa based on total fluidized solid present is maintained in the generation zone at all times.

10. A process for producing S02 which comprises intimately contacting iron sulfide ore in finely-divided form with finely-divided FeaOs in a generation zone at a temperature of 600 C. to 900 C. whereby reaction sets in between the FezOs and the sulfur-containing ore to form S02 and F8304 but without conversion of all of the sulfur present to S02, passing S02 vapors upwardly through the finely-divided solids in the generation zone at a rate sufficient to maintain said solids as a dense turbulent fluidized mass, withdrawing a stream of substantially pure $02 from the generation zone, withdrawing a stream of solids containing Fe3O4 and unconverted sulfur from the generation zone, introducing the withdrawn stream of solids to a separate clean-up zone, contacting the stream of solids in the clean-up zone with enough of an oxygen-containing gas to convert the remaining sulfur to S02 without substantial reoxidation of the Fes04 to F6203, and separately recovering a stream of dilute S02 from the clean-up zone.

11. A process according to claim 10 in which the sulfur-containing ore is pyrites, the oxygen-containing gas is air, and in which a portion of the stream of substantially pure S02 is mixed with the stream of dilute S02.

12. A process according to claim 11 in which the solids converted in said clean-up zone and consisting essentially of pure iron oxide are reoxidized with an oxygencontaining gas in a reoxidation zone to F6203 at a temperature higher than the said generation zone temperature but below the sintering temperature of the solids being reoxidized, the reoxidized FezOs is Withdrawn from said reoxidation zone, purged of reoxidation zone gases by means of S02 vapors and re-introduced into the generation zone while fluidized in S02.

13. In a process for producing S02 wherein sulfidic iron ore is reacted with finely-divided FezOs so as to form S02 and a hot solid granular material containing iron sulfide and F8304, the steps which comprise continuously charging said hot granular solid material containing iron sulfide and FesOr into a turbulent dense bed formed of said material and FezOa supported on a grid in a reaction zone, continuously introducing air upwardly through said grid into the reaction zone under suflicient pressure to maintain a fluidized bed and in an amount sufficient to oxidize Fe304, to FezOs whereby the FeaOq. is oxidized to FezOa and sulfur contained in the iron sultide is converted to S02, removing excess heat from said reaction zone by indirect cooling to maintain temperatures sufficient to produce S02 but below the sintering temperature of the iron compounds in said bed and withdrawing S02-containing gas from said reaction zone, and

continuously independently withdrawingFezOs directly from a portion of the dense bed in said reaction zone.

14. A process in accordance with claim 13, wherein the sulfide in said hot granular solid material charged to said reaction zone is FeS.

References Cited in the file of this patent UNITED STATES PATENTS 1,447,645 Chase Mar. 6, 1923 1,730,514 Levy Oct. 8, 1929 1,941,592 Bacon Jan. 2, 1934 1,947,776 Huff Feb. 20, 1934 2,009,733 Hechenbleikner July 30, 1935 2,039,645 Hechenbleikner May 5, 1936 2,084,697 McClusky June 22, 1937 2,209,331 Haglund July 30, 1940 2,444,990 Hernrninger July 13, 1948 2,494,337 Hernminger Jan. 10, 1950 2,536,099 Schleicher Ian. 2, 1951 2,586,818 Herms Feb. 26, 1952 2,591,595 Ogorzaiy Apr. 1, 1952 2,637,629 Lewis May 5, 1953 (Other references on following page) 9 10 FOREIGN PATENTS Smith: Inorganic Chemistry, pages 401, 402, Apple- 161,581 Great Britain Apr. 14, 1920 Century 1937- 597,221 G Ja I 21, 1948 Kalbach: Chemical and Metallurglcal Engineering,

rea n am n June 1944, pages 94 9s, Fluidization. OTHER REFERENCES 5 Mellor: Treatise on Inorganic Chemistry, vol. 10, page 188, Longmans, Green and Co., 1930. 

3. A PROCESS FOR PRODUCING SO2 SUBSTANTIALLY FREE OF SULFUR TRIOXIDE, OXYGEN, NITROGEN, AND ELEMENTAL SULFUR WHICH COMPRISES INTIMATELY CONTACTING A NORMALLY SOLID NATURALLY-OCCURRING SULFUR-CONTAINING MATERIAL IN A GENERATION ZONE WITH A FINELY-DIVIDED SOLID METAL OXIDE HAVING AN OXIDIZING POTENTIAL SUFFICIENT TO OXIDIZE SULFUR SUBSTANTIALLY COMPLETELY TO SO2 BUT INSUFFICIENT FOR SULFUR OXIDATION BEYOND SO2, AT AN OXIDIZING TEMPERATURE ABOVE ABOUT 600* C. BUT BELOW THE SINTERING TEMPERATURE OF THE METAL OXIDE, WHEREBY THE OXYGEN OF THE METAL OXIDE REACTS WITH THE SULFUR OF SAID SULFUR-CONTAINING MATERIAL TO FORM SO2 AND A METAL OXIDE OF REDUCED OXYGEN CONTENT, PASSING SO2 VAPORS UPWARDLY THROUGH THE FINELYDIVIDED SOLID OXIDE IN THE GENERATION ZONE AT A RATE SUFFICIENT TO MAINTAIN SAID OXIDE AS A DENSE TURBULENT FLUIDIZED MASS, WITHDRAWING SO2 FROM THE GENERATION ZONE, REMOVING THE METAL OXIDE OF REDUCED OXYGEN CONTENT TO A SEPARATE REGENERATION, REOXIDIZING THE WITHDRAWN OXIDE BY CONTACTING THE SAME WITH AN OXYGEN-CONTAINING GAS IN THE REGENERATION ZONE, PURGING THE REOXIDIZED OXIDE WITH SO2 AND RETURNING THE REOXIDIZED OXIDE FLUIDIZED IN SO2 TO THE GENERATION ZONE. 